New Obesity Drug Hits the Market

After a long wait, patients now have a choice between two new obesity drugs. They couldn't be more different.

Arena Pharmaceuticals' Belviq, the newest offering, looks relatively safe. The top adverse reactions were headaches, followed by dizziness and fatigue -- nothing to be too worried about. The downside is that patients didn't lose all that much weight while taking Belviq compared to the placebo group. After one year, in two combined phase 3 studies, patients lost a placebo-adjusted 3.3% of their body weight. Belviq, which will be marketed by Arena's partner Eisai, should hit pharmacy shelves beginning on Tuesday.

Qsymia, sold by VIVUS , has been on the market since September. It produces substantially more weight loss: at the highest dose, 9.4% placebo adjusted in one study, and 8.6% placebo adjusted in another. Unfortunately, that weight loss comes with additional risks, including the potential to cause birth defects if taken by women who become pregnant.

Which one will end up winning? I see a place for both drugs. We could see patients starting on Belviq, and then moving to Qsymia if they don't see satisfactory results. Morbidly obese patients might start directly on Qsymia, because they desperately need to lose a large amount of weight. Piddling around with 3% isn't going to cut it.

While the companies are clearly competing against each other, having another drug on the market may actually benefit VIVUS, because there will be more sales reps beating the "take drugs for weight loss" drum. Despite the large number of patients, few get drugs as their treatment. Increasing their use should expand the overall market.

Conversely, having VIVUS go first likely helped Arena and Eisai. Getting insurers to cover the drugs is the key to sales. VIVUS saw an abandonment rate of 30% when it first launched, likely because of sticker shock from those not covered by insurance. Qsymia, having already gone through the insurers' review process for coverage, likely made it easier for Eisai to gain reimbursement for Belviq.

The third player, Orexigen , could end up finding a fit, too; its obesity drug Contrave appears to have a benefit and side effect profile somewhere in between Qsymia and Belviq. The company is still testing Contrave to confirm it doesn't cause heart problems, so it probably won't be on the market until next year at the earliest. With the extra safety data, Contrave might actually take the lead as the go-to drug.

And Orexigen will have Eisai, Arena, and VIVUS to thank for setting the stage.

Who will win the obesity drug market?Can VIVUS pick up its lagging sales and fend off the competition, or will Arena Pharmaceuticals reign supreme in the obesity space? If you're in the dark, grab copies of The Motley Fool's premium research reports on VIVUS and Arena Pharmaceuticals to stay up to date. The reports give investors the must-know information, including an in-depth look at the obesity market and reasons to buy and sell both stocks. Click now for an exclusive look at Arena and VIVUS -- complete with a full year of free updates -- today.